In March 1979, equipment failure and operator errors led to a partial core meltdown of one of Three Mile Island’s two reactors. The damaged reactor has been mothballed since then but the other reactor is still in use.

The owner of Three Mile Island, Exelon, said operating costs for just one unit at the plant were high, further damaging Three Mile Island’s financial viability in a time of competition from natural gas and renewable energies.

The Chicago-based company’s announcement comes after what it called more than five years of losses and a recent failure in a capacity auction to sell Three Mile Island power into the regional grid. Exelon wants Pennsylvania to give nuclear power the kind of preferential treatment given to energy sources such as wind and solar.

Exelon and other nuclear power plant owners have made the pitch that zero-carbon nuclear plants are better suited than natural gas or coal to fight climate change. So-called nuclear bailouts have won approval in Illinois and New York but the potential for higher utility bills in Pennsylvania is drawing pushback from energy companies, manufacturers and consumer advocates.

“Like New York and Illinois before it, the commonwealth has an opportunity to take a leadership role by implementing a policy solution to preserve its nuclear energy facilities and the clean, reliable energy and good-paying jobs they provide,” Exelon’s president and chief executive, Chris Crane, said in a statement.

Nuclear power plants have been hammered by the natural gas boom, which has slashed electricity prices, flooding the market from the north-east’s Marcellus Shale reservoir, the nation’s most prolific gas field. Meanwhile, electricity consumption hit a wall after the recession, while states have emphasized renewable energies and efficiency.

With the rapid growth of natural gas power in Pennsylvania and elsewhere, closing Three Mile Island would have little or no impact on electricity bills, analysts say. But it may be replaced by carbon-emitting power sources such as coal or natural gas. Pennsylvania is the nation’s No 2 nuclear power state, after Illinois.

FirstEnergy has said it could decide next year to sell or close its three nuclear plants – Davis-Besse and Perry in Ohio and Beaver Valley in Pennsylvania. PSEG of New Jersey owns all or parts of four nuclear plants, but it has said it will not operate long-term money losers.

Christina Simeone, of the Kleinman Center for Energy Policy at the University of Pennsylvania, said the mid-Atlantic grid operator PJM and the US Department of Energy had taken first steps toward policies or recommendations that could help nuclear power plants.

“I definitely think they are responding to some profound changes in the market as a result of very low prices for natural gas and hyper-competitive natural gas resources,” Simeone said.